• Title/Summary/Keyword: Thermo-Stability

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Critical Factors to High Thermostability of an ${\alpha}$-Amylase from Hyperthermophilic Archaeon Thermococcus onnurineus NA1

  • Lim, Jae-Kyu;Lee, Hyun-Sook;Kim, Yun-Jae;Bae, Seung-Seob;Jeon, Jeong-Ho;Kang, Sung-Gyun;Lee, Jung-Hyun
    • Journal of Microbiology and Biotechnology
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    • v.17 no.8
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    • pp.1242-1248
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    • 2007
  • Genomic analysis of a hyperthermophilic archaeon, Thermococcus onnurineus NA1 [1], revealed the presence of an open reading frame consisting of 1,377 bp similar to ${\alpha}$-amylases from Thermococcales, encoding a 458-residue polypeptide containing a putative 25-residue signal peptide. The mature form of the ${\alpha}$-amylase was cloned and the recombinant enzyme was characterized. The optimum activity of the enzyme occurred at $80^{\circ}C$ and pH 5.5. The enzyme showed a liquefying activity, hydrolyzing maltooligosaccharides, amylopectin, and starch to produce mainly maltose (G2) to maltoheptaose (G7), but not pullulan and cyclodextrin. Surprisingly, the enzyme was not highly thermostable, with half-life ($t_{1/2}$) values of 10 min at $90^{\circ}C$, despite the high similarity to ${\alpha}$-amylases from Pyrococcus. Factors affecting the thermostability were considered to enhance the thermo stability. The presence of $Ca^{2+}$ seemed to be critical, significantly changing $t_{1/2}$ at $90^{\circ}C$ to 153 min by the addition of 0.5 mM $Ca^{2+}$. On the other hand, the thermostability was not enhanced by the addition of $Zn^{2+}$ or other divalent metals, irrespective of the concentration. The mutagenetic study showed that the recovery of zinc-binding residues (His175 and Cys189) enhanced the thermo stability, indicating that the residues involved in metal binding is very critical for the thermostability.

Thermo-structural Effects of Thermal Barrier Coating on Regenerative Cooling Chamber (열차폐 코팅이 재생냉각 챔버에 미치는 열/구조적인 영향)

  • Ryu, Chul-Sung;Lee, Keum-Oh;Kim, Hong-Jip;Choi, Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.421-425
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    • 2009
  • A study has been performed to investigate the thermo-mechanical effects of thermal barrier coating on liquid rocket regenerative cooling chamber using finite element analysis. Two kinds of thermal barrier coatings were studied on the same loading condition: first, NiCrAlY-$ZrO_2$, coating which is currently applied to the developing combustion chamber and second, Ni-Cr coating which might be applied in the future. Analysis results showed that NiCrAlY-$ZrO_2$ coating has better decreasing effect of temperature than the Ni-Cr coating. As a results, temperature and deformation of the cooling channel in the NiCrAlY-$ZrO_2$ coating were also less than those of the Ni-Cr coating. The Ni-Cr coating has no effect on a structural stability of the outer jacket but the NiCrAlY-$ZrO_2$ coating reduced the effective stress of the outer jacket and enhanced the structural stability of the chamber.

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Case Studies on the Experiments for Long-Term Shear Behavior of Rock Discontinuities (암반 내 불연속면의 장기 전단 거동 평가를 위한 고찰)

  • Juhyi Yim;Saeha Kwon;Seungbeom Choi;Taehyun Kim;Ki-Bok Min
    • Tunnel and Underground Space
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    • v.33 no.1
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    • pp.10-28
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    • 2023
  • Long-term shear behavior of the rock discontinuities should be analyzed and its stability should be evaluated to ensure the long-term stability of a high-level radioactive waste disposal repository. The long-term shear behavior of the discontinuities can be modeled with creep and RSF models. The shear creep test, velocity step test, and slide-hold-slide test can be performed to determine their model parameters or analyze the shear behavior by experiments under various conditions. Testing apparatuses for direct shear, triaxial compression, and biaxial shear were mainly used and improved to reproduce the thermo-hydro-mechanical conditions of local bedrock, and it was confirmed that the shear behavior could vary. In order to design a high-level radioactive waste disposal site in Korea, the long-term behavior of rock discontinuities should be investigated in consideration of rock types, thermo-hydro-mechanical conditions, metamorphism, and restoration of shear resistance.

Evaluation of Thermal Aging on PVC Using Thermo Gravimetry Analysis and Accelerated Thermal Aging Test (TGA와 가속열화를 이용한 전선 피복용 PVC의 열적 열화평가)

  • 박형주;김기환;김홍
    • Fire Science and Engineering
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    • v.18 no.3
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    • pp.45-50
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    • 2004
  • Thermal degradation of PVC which used for insulator of 600V vinyl insulated wire has been studied by thermo gravimetry analysis and accelerated thermal aging test. The activation energy using thermo gravimetry analysis was determined by the kinetic methods, such as Kissinger and Flynn-Wall-Ozawa. The activation energy was determined to from 89.29 kJ/mol to 111.39 kJ/mol in 600V PVC insulated wire and from 97.80 kJ/mol to 119.25 kJ/mol in 600v heat-resistant PVC insulated wire. And also, the activation energy through a long-term thermal aging test was calculated by using Arrhenius equation In the low temperature of 8$0^{\circ}C$, 9$0^{\circ}C$, 10$0^{\circ}C$. The results showed that 600V PVC insulated wire was 92.16 kJ/mol, and 600v heat-resistant PVC insulated wire was 97.52 kJ/mol. Consequently, the activation energy of 600V heat-resistant PVC insulated wire is larger than 600V PVC insulated wire. Therefore, it can be predicted that 600V heat-resistant PVC insulated wire has a long-term stability relatively.

Phase Formation and Thermo-physical Properties of Lanthanum/Gadolinium Zirconate with Reduced Rare-earth Contents for Thermal Barrier Coatings (열차폐코팅을 위한 희토류가 저감된 란타눔/가돌리늄 지르코네이트의 상형성 및 열물성)

  • Lee, Sujin;Kwon, Chang-Sup;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Nahm, Sahn;Kim, Seongwon
    • Journal of Powder Materials
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    • v.22 no.6
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    • pp.420-425
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    • 2015
  • Rare-earth zirconates, such as lanthanum zirconates and gadolinium zirconates, have been intensively investigated due to their excellent properties of low thermal conductivity as well as chemical stability at high temperature, which can make these materials ones of the most promising candidates for next-generation thermal barrier coating applications. In this study, three compositions, lanthanum/gadolinium zirconates with reduced rare-earth contents from stoichiometric $RE_2Zr_2O_7$ compositions, are fabricated via solid state reaction as well as sintering at $1600^{\circ}C$ for 4 hrs. The phase formation, microstructure, and thermo-physical properties of three oxide ceramics are examined. In particular, each oxide ceramics exhibits composite structures between pyrochlore and fluorite phases. The potential of lanthanum/gadolinium zirconate ceramics for TBC applications is also discussed.

Phase Evolution and Thermo-physical Properties of Rare-earth Oxides for Thermal Barrier Systems (열차폐용 희토류 산화물의 상형성과 열물성)

  • Shim, Byung-Chul;Kwak, Kil-Ho;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Jang, Byung-Koog;Kim, Seong-Won
    • Journal of Powder Materials
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    • v.17 no.2
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    • pp.148-153
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    • 2010
  • Thermal barrier systems have been widely investigated over the past decades, in order to enhance reliability and efficiency of gas turbines at higher temperatures. Yttria-stabilized zirconia (YSZ) is one of the most leading materials as the thermal barriers due to its low thermal conductivity, thermodynamic stability, and thermal compatibility with metal substrates. In this work, rare-earth oxides with pyrochlore phases for thermal barrier systems were investigated. Pyrochlore phases were successfully formed via solid-state reactions started from rare-earth oxide powders. For the heat-treated samples, thermo-physical properties were examined. These rare-oxide oxides showed thermal expansion of $9{\sim}12{\times}10^{-6}/K$ and thermal conductivity of 1.2~2.4 W/mK, which is comparable with the thermal properties of YSZ.

The appearance change and heat·moisture transfer properties of knitted fabric by yarn shrinkage (원사의 수축에 따른 다공성 편성물의 형태변화와 열·수분 전달특성)

  • Sang, Jeong-Seon;Park, Juhyun;Lee, Mee-Sik;Oh, Kyung Wha
    • The Research Journal of the Costume Culture
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    • v.25 no.6
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    • pp.880-892
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    • 2017
  • In this study, the appearance change and the heat moisture transfer properties of knitted fabric by yarn shrinkage were examined to obtain useful data on the development of thermo-sensitive functional materials. Eleven types of knitted fabric were knitted using highly bulky acrylic-blended yarn. After shrinking the specimens using dry heat treatment, the appearance change and thickness were measured. An HEC simulator was adopted for measuring the heat moisture transfer properties of specimens by yarn shrinkage. When holes were arranged vertically in the mesh structure, the specimens with 2,500 and 5,000 holes showed high percent change of hole area, appearance, and thickness. When holes were diagonally arranged in the mesh structure, the percent change of hole area in the specimen with 1,250 holes was larger than the one with 2,500 holes. However, the dimensional stability of the specimen with 2,500 holes was better because of its smaller appearance and thickness change. In the tuck structure, the percent change of hole area in the specimen with 625 and 416 holes was relatively large compared with the appearance and thickness change. Furthermore, the hole size in the tuck structure was smaller than that in the mesh structure but the percent change of hole area was larger. Therefore, it was proved that the tuck structure is more suitable than the mesh structure for developing thermo-sensitive functional materials. Heat moisture transfer property test verified that the change of hole area by yarn shrinkage enabled obtaining the thermal effect due to the distinct temperature difference in the inner layer.

Poly(vinyl alcohol) Nanocomposite Films (II): Thermo-mechanical Properties and Morphology (폴리(비닐 알코올) 나노복합체 필름(II) : 열적-기계적 성질 및 모폴로지)

  • Ham, Shin-Kyun;Jung, Min-Hye;Chang, Jin-Hae
    • Polymer(Korea)
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    • v.30 no.6
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    • pp.545-549
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    • 2006
  • Blends of poly(acrylic acid- co-maleic acid) (PAM) with poly (vinyl alcohol) (PVA) were pre -pared in distilled water PVA/PAM/saponite (PVA/PAM/SPT) nanocomposite films were prepared with various clay contents by using the solution intercalation method. The variations of the dispersion, morphology, and thermo-mechanical properties of the nanocomposites with clay content in the range 0 to 9 wt% were examined. Up to 3 wt% clay loading, the clay particles were homogeneously dispersed in the PVA/PAM blends. However, some agglomerated structures form in the polymer matrix above a clay content of 7 wt%. The thermal stability of the hybrids was increased linearly with increasing the clay loading up to 9 wt%. The maximum strength and modulus were obtained at a clay content of 7 wt%. Thus, the addition of small amounts of clay to the PVA/PAM blends produced PVA/PAM nano-composites with improved the thermo-mechanical properties.

Phase Formation and Thermo-physical Properties of GdO1.5-ZrO2 System for Thermal Barrier Coating Application (열차폐코팅용 GdO1.5-ZrO2계 희토류 지르코네이트 세라믹스의 상형성과 열물리 특성)

  • Kim, Sun-Joo;Lee, Won-Jun;Kwon, Chang-Sup;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Im, Dae-Soon;Kim, Seongwon
    • Journal of the Korean Ceramic Society
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    • v.51 no.6
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    • pp.554-559
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    • 2014
  • Gadolinium zirconate, $Gd_2Zr_2O_7$, is one of the most promising candidates for replacing yttira-stabilized zirconia (YSZ) in thermal barrier coating (TBC) applications due to its low thermal conductivity and chemical stability at high temperature. In this study, rare-earth zirconate ceramics in the $GdO_{1.5}-ZrO_2$ system with reduced gadolinia contents were fabricated via solid-state reaction as well as hot-pressing at $1800^{\circ}C$. The phase formation, microstructure, and thermo-physical properties of these oxides were examined. The potential application of $GdO_{1.5}-ZrO_2$ ceramics for TBC was also discussed.

Thermo-structural Analysis for Radiation-Cooled Nozzle Extension of Thrust Chamber (복사냉각방식 연소기 노즐확장부 열/구조해석)

  • Ryu, Chul-Sung;Lee, Keum-Oh;Choi, Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.04a
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    • pp.291-295
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    • 2011
  • Thermo-structural analysis was performed for a radiation-cooled nozzle extension of thrust chamber. A Niobium alloy that is known to be a high-performance refractory alloy was used. Since area ratio of the nozzle extension is larger than that of nozzle divergence part, its size also becomes larger. For this reason, it is important to minimize the thickness of nozzle extension to reduce its weight. For the purpose of weight minimization, the thickness of nozzle extension was varied from 1.0 mm to 0.4 mm and structural stability was evaluated for each case. Analysis results showed that nozzle extension with thickness of 0.4 mm is structurally stable for the operation condition. The effect of combustion-included vibration will be additionally considered in the future.

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